Pages

Monday, March 30, 2009

IAU Circular No. 9031, issued on 2009 Mar 20, announces the recovery of comet P/2001 MD_7 = COMET P/2009 F3 (LINEAR) by the undersigneds; it was last observed in April 2002.

We picked up this object on 2009 Mar 17, 18 and 20 through a couple of remotely controlled telescopes, located in New Mexico and Australia. The comet appeared as a pale glow, magnitude about 18, nearly 15 arcsec in diameter.

The recovered comet was very close to the ephemerids positions, however its detection has been a little problematic, because it was rather low in the morning sky just before twilight, located in a rich star field in Sgr. We took several nights of observations to locate it, fighting with clouds and moonlight interference.

According the orbital elements published by the Minor Planet Center, perihelion will occur in September 2009, with the comet at 1.25 AU from the Sun; at that time P/2009 F3 (LINEAR) will reach about magnitude 12. This object moves along an elliptic orbit in 7.9 years, having a semi-major axis of 3.97 AU, eccentricity of 0.68 and an inclination nearly 13.5 deg.

We thanks the Mayhill-GRAS and Grove Creek-Skylive staff for the kind support they provided us for this tricky recovery.

Sunday, March 15, 2009

We performed some follow-up of this object while it was posted in the NEO-CP.

Since the candidate was too low to be imaged from the Remanzacco Observatory (MPC #473), on 2009, Mar. 15.1 we connected to the GRAS network, and imaged it remotely from Mayhill (NM), details on image:

The initial stacking produced a trailed image of the central condensation, because the expected proper motion was slightly off. After some trials, we found the suitable speed and PA able to produce a sharp image of the comet.

Stacking our frames (co-adding of 30 unfiltered exposure, 30 seconds each) we noticed an obvious comet, with a central condensation having about magnitude 14.6 (unfiltered R), a bright inner coma, having a diameter of about 1.4 arcmin, and faint external halo nearly 4 arcmin in diameter, slightly elongated toward South-West. The total magnitude m1 we measured was about about 11.0 (unfiltered R).

we understand that this comet moves along a parabolic, retrograde, orbit (i= 126 deg, q= 0.6 AU). Perihelion will be reached in the beginning of next April 2009, with m1 about 10. Unfortunalety comet ITAGAKI will stay at small elongation from the Sun, so it will be a difficult object to be observed.

K. Itagaki found it from his private observatory of Takanezawa-Tochigidi with a 0,2-m f/3, reflector + CCD camera at (about) 09h UT on 2009, March, 14.

Congratulations to Itagaky-san for his nice gift: there are still some opportunities for dedicated amateur comet catchers, in spite of the professional surveys!

Wednesday, March 11, 2009

Comet C/2007 N3 (LULIN) was a nice show in late February this year, when it passed relatively close (nearly 0.42 AU, on Feb. 24th). At about its perigee, another phenomena occurred: its phase angle reached a minimum value, then it quickly started to grow-up again. Nearly simultaneosly we witnessed an abrupt change in the appearance of the comet, due to the consequent foreshortening effect: the ion tail, in a matter of hours, switched from North-West to South-East.

Possibly another, less cospicuous, change in comet's LULIN aspect may be under course: according to our follow-up, some effects of the foreshortening change seems to be readily visible also in a series of images we secured from various sites & through with different scopes, in the past few weeks.

As you may notice from the following panels, the prominent feature (kind of "fan" structure) originating from the central condensation toward South-West (i.e. at about PA 220 deg), plus a secondary one, toward North-East (i.e. at about PA40 deg) that was reported by several observers, visible till March 2nd, now seems to be over:

More data need to be secured to definitely clarify the situation, however at a first glance we have the impression that this might be a foreshortening effects as well. Apparently, the changing geometry really plays a strong role, when interpreting the inner coma details sometimes reported on comets (alleged fans, jets, etc.).

Monday, March 9, 2009

Through image processing, the comet show a funny effect: at low contrast, an asymmetric coma is seen, about 45 arcsec in diameter, with an obvious elongation toward (about) East (PA 90 deg). In high contrast, a broad tail, nearly 80 arcsec long, became obvious; but it points toward South-West, at about PA 230 deg (i.e., in nearly opposite direction)!

Few days later, on 2009, Mar. 2nd, about 13h40m UT, it made a close approach with Earth, passing only 72,000 Km away (i.e. 1/5th of the Earth-Moon distance, and about twice the height of geostationary satellites).

When we shoot our image, a couple of hours before its closest approach, this rock (about 35-m in diameter) was speeding at about 9 deg/hour in the southern constellation of Vela, shining at about magnitude 12. The 5 seconds exposure time was more than enough to record its trail among the field stars (details on image):

Comets & Asteroids news

Welcome to our Astronomy blog, devoted in particular to Comets & Asteroids and related topics. This blog is maintained by Italian amateur astronomer Ernesto Guido, particularly active in the study of the small bodies of the Solar System.